This invention belongs to the field of lubricants. More particularly, this invention relates to certain improved poly xcex1-olefins prepared from a mixed feed of olefins.
Poly xcex1-olefins comprise one class of hydrocarbon lubricants which has achieved importance in the lubricating oil market. These materials are typically produced by the polymerization of xcex1-olefins typically ranging from 1-octene to 1-dodecene, with 1-decene being a preferred material, although polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins, as described in U.S. Pat. No. 4,956,122 and the patents referred to therein. The poly xcex1-olefin (PAO) products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2 cSt at 100xc2x0 C. to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100xc2x0 C. The PAO""s may be produced by the polymerization of olefin feed in the presence of a catalyst such as AlCl3, BF3, or BF3 complexes. Processes for the production of PAO lubricants are disclosed, for example, in the following patents: U.S. Pat. Nos. 3,382,291; 4,172,855; 3,742,082; 3,780,128; 3,149,178; and 4,956,122. The PAO lubricants are also discussed in Lubrication Fundamentals, J. G. Wills, Marcel Dekker Inc., (New York, 1980). Subsequent to the polymerization, the lubricant range products are hydrogenated in order to reduce the residual unsaturation. In the course of this reaction, the amount of unsaturation is generally reduced by greater than 90%.
A major trend in passenger car engine oil usage is the extension of oil drain intervals. Thus, a need exists for low viscosity PAO""s which exhibit low Noack volatility. (See ASTM D 5800 Standard Test Method for Evaporation Loss of Lubricating Oils by the Noack Method.)
The properties of a particular grade of PAO are greatly dependent on the xcex1-olefin used to make that product. In general, the higher the carbon number of the xcex1-olefin, the lower the Noack volatility and the higher the pour point of the product.
PAO""s having a viscosity of 4 cSt are typically made from 1-decene and have a Noack volatility of 13-14% and pour point of  less than xe2x88x9260xc2x0 C. PAO""s having a viscosity of 6 cSt are typically prepared from 1-decene or a blend of xcex1-olefins and have a Noack volatility of about 7.0% and pour point of about xe2x88x9260xc2x0 C.
The present invention relates to poly xcex1-olefins (PAO""s) which exhibit superior Noack volatility, while maintaining good low temperature properties. Mixtures of 1-decene and 1-dodecene are polymerized using BF3 promoted alcohol/ester mixture. The reaction mixture is distilled to remove the unreacted monomeric and dimeric species. The resulting product is hydrogenated to saturate the oligomers, to provide a product having a viscosity of 5 cSt. This product is distilled and distillation cuts blended to provide PAO""s of varying viscosity grades. The 4 cSt PAO is comprised mostly of trimers and tetramers while the 6 cSt is comprised of trimers, tetramers, and pentamers.